The present invention pertains generally to injectors for delivering a medicament into a patient. More particularly, the present invention pertains to needleless injectors having a vacuum system for applying a suction at the interface between the injector and the skin of the patient. The present invention is particularly, but not exclusively, useful for controlling the vacuum system of a needleless injector during the administration of a dose of medicament to a patient.
Historically, most injections have been performed using traditional hypodermic syringes. More recently, diseases caused by the transmission of bloodborne pathogens such as HIV and hepatitis have caused the health care industry to closely examine the safety of traditional hypodermic syringes. Because of the fatal nature of AIDS and the lack of a suitable cure, exposing health care workers to contaminated needles and other sharps is now considered unacceptable. Needleless injectors offer an alternative to traditional hypodermic syringes.
Needleless injectors are less likely to accidentally transmit bloodborne pathogens from a patient to a health care worker than traditional hypodermic syringes for several reasons. First, only the medicament and not the needleless injector actually penetrates the patient, thus, the needleless injector is unlikely to become contaminated with bloodborne pathogens during use. Also, a contaminated needleless injector is unlikely to transmit a bloodborne pathogen to a health care worker because the needleless injector does not have any sharp surfaces to expose the blood of the health care worker. Additionally, accidental needlesticks often occur while capping or covering the needle. Thus, these types of accidents are obviated by the use of a needleless injector.
In overview, a needleless injector typically includes a chamber for holding an injectable medicament. At the tip of the injector, an opening is provided in the chamber for transferring medicament from the chamber and into the patient. A plunger and a mechanism for rapidly forcing the plunger into the chamber are generally included to force the medicament through the opening and out the tip of the injector. In use, the tip of the injector is placed in contact with the skin of the patient and the plunger is forced into the chamber. In response, the medicament flows through the opening and out of the tip of the injector, first creating a hole in the skin of the patient. Once a hole in the skin is created, the remaining medicament flows though the hole and into the patient.
Important for the present invention, suction can be used to hold the tip of the injector against the skin. For example, U.S. Pat. No. 5,911,703 entitled xe2x80x9cTwo-Stage Fluid Medicament Jet Injectorxe2x80x9d that issued to Slate et al. on Jun. 15, 1999 and which is assigned to the same assignee as the present invention, discloses an injector with an integral suction compartment for pulling the skin against the injector tip. As disclosed, the suction compartment functions to create a seal between the skin area and the injector tip without having to compress the skin area and underlying tissue. Further, the use of a suction compartment can prevent lacerations that can be caused when the injector tip moves relative to the skin during an injection. Also, the suction compartment can function to create a subcutaneous pocket facilitating infusion of the medicament. Another important function of the suction compartment is to provide a seal around the tip of the syringe to enable slow delivery of the medicament.
It is apparent from the above discussion that inadvertent triggering of the injector before the injector is positioned and the suction is applied should be avoided. Also, during an injection, the suction should be maintained to ensure a stable interface between the injector tip and the skin. Thus, control of the vacuum system to provide suction at the skin/injector tip interface is crucial to ensuring a safe, efficient medicament transfer using a needleless injector.
In light of the above, it is an object of the present invention to provide a vacuum control system for a needleless injector in which a single control movement by the user releases a mechanical trigger lock and activates the vacuum motor. Another object of the present invention is to provide a vacuum control system for a needleless injector that is configured to deactivate the vacuum motor if the vacuum switch is released by the user before the triggering of an injection. It is another object of the present invention to provide a vacuum control system for a needleless injector which maintains suction at the interface between the injector and the skin of the patient during injection of the medicament in spite of the inadvertent release of the vacuum activation switch by the user. It is yet another object of the present invention to provide a vacuum control system for a needleless injector that automatically deactivates the vacuum motor after the injection of the medicament into the patient is completed thereby giving the user an indication that the injection is complete and that it is safe to remove the injector from the skin. Still another object of the present invention is to provide a vacuum control system for a needleless injector that functions over the wide range of voltages produced by a typical battery. Another object of the present invention is to provide a vacuum control system for a needleless injector that provides a steady voltage to the vacuum motor during the injection. Still another object of the present invention is to provide a vacuum control system for a needleless injector that draws a minimal amount of power from the battery during periods between use, when the injector is uncocked. Yet another object of the present invention is to provide a vacuum control system for a needleless injector which is easy to use, relatively simple to implement, and comparatively cost effective.
The present invention is directed to a vacuum control system for a jet injector. For the present invention, the control system includes a user operable switch and a mechanical switch. An electrical circuit connects these two switches, with a vacuum pump and a battery to control the vacuum at the injector tip during an injection procedure. In the preferred embodiment of the present invention, the user operable switch also functions as a safety release button for the injector to ensure that a vacuum has been established at the injector tip prior to initiating an injection.
For the present invention, the vacuum control system interacts with a jet injector which has an internal mechanical switch. The mechanical switch is configured to automatically close and thereby shut off the vacuum upon completion of an injection. Specifically, the mechanic switch includes a conductive drive bar that travels within the hollow tube of the injector during an injection. A conductive, inner barrel is positioned near the distal end of the injector tube for contact with the drive bar upon completion of an injection. The contact between the drive bar and inner barrel closes the mechanical switch. A cocking mechanism is provided for repositioning the drive bar back to the proximal end of the tube to allow for a subsequent injection. This movement of the drive bar to the proximal end of the tube opens the mechanical switch.
As described above, the electrical circuit has a first switch and a second switch for controlling the operation of the vacuum system. The first switch is user operable and is moveable between an ON position wherein current flows through the switch (i.e. the first switch is closed) and an OFF position. A return spring is provided to bias the first switch in the OFF position. The second switch is established by the contact of the inner barrel with the drive bar. When the inner barrel contacts the drive bar, the second switch is in the ON position and current flows through the switch (i.e. the second switch is closed). Conversely, when the inner barrel is separated from the drive bar, the second switch is in the OFF position and no current flows through the switch (i.e. the second switch is closed).
For the present invention, the electrical circuit is configured to pass current from the power source to the vacuum pump when the first switch is in its ON position and the second switch is in its OFF position. Further, the electrical circuit is configured to prevent current from passing through the vacuum pump when the first switch is in its ON position and the second switch is in its ON position. Additionally, the electrical circuit is configured to prevent current from passing through the vacuum pump whenever the first switch is in its OFF position.
The user operable switch also functions as a safety release button for a firing cap located at the proximal end of the injector tube. For the present invention, an interlock ring that is rotatable about the longitudinal axis of the tube is interposed between the proximal end of the tube and the firing cap. The interlock ring is attached to the user operable switch for rotation about the longitudinal axis of the tube in response to movements of the user operable switch. A tab projects proximally from the interlock ring for engagement with a slot formed in the firing cap near the distal end of the firing cap. When the user operable switch is depressed (i.e. moved to its ON position), the interlock ring is rotated to align the tab of the interlock ring with the slot of the firing cap. With the slot and tab aligned, the firing cap is armed (i.e. capable of being depressed to release the drive bar). The return spring, which biases the user operable switch in the OFF position, also biases the interlock ring into a position where the tab and slot are misaligned to thereby lock the firing cap whenever the user operable switch is not depressed by the user.
In the operation of the present invention, the jet injector is initially uncocked. In the uncocked configuration, both switches are in the ON position (the reason for this will become apparent below), and consequently, the vacuum pump is inactive. Upon cocking the injector, the cocking mechanism will position and hold the drive bar near the proximal end of tube placing the second switch in the OFF position. Further, the cocking mechanism will move the firing cap until the firing cap is positioned proximally to the interlock ring. As such, the return spring will cause both the user operable switch to move into the OFF position and the interlock ring to move to a position where the tab of the interlock ring and the slot of the firing cap are misaligned. Thus, immediately after cocking the injector, the vacuum pump is inactive (because both switches are OFF) and the firing cap is locked.
Once the injector is in the cocked configuration, the user can position the injector tip to a preselected area of skin and depress and hold the user operable switch. Upon depressing the user operable switch, the vacuum pump will be activated (first switch ON, second switch OFF) to provide suction at the injector tip. Further, as indicated above, the firing cap will be armed. At this point, release of the user operable switch will deactivate the vacuum pump, allowing the user to reposition the injector tip. Specifically, upon release of the user operable switch the return spring will cause both the user operable switch to return to the OFF position and the interlock ring to return to a position where the firing cap will be disarmed and locked.
While the user operable switch is depressed and held by the user, the vacuum pump remains activated and the firing cap remains armed. Thus, by holding the user operable switch ON and depressing the firing cap, the user can inject the medicament. Upon depressing the firing cap, the drive bar is released. Further, depressing the firing cap causes the tab of the interlock ring to extend into the slot in the firing cap. Importantly, this prevents the interlock ring from rotating. As such, after the firing cap is depressed, the user operable switch is held in the ON position due to the inability of the interlock ring to rotate. The consequence of this is that once the user depresses the firing cap, the vacuum pump remains activated for the entire duration of the injection, regardless of the whether the user releases the user operable switch.
As indicated above, depressing the firing cap causes the drive bar to translate along the tube. Specifically, the drive bar travels until it contacts the inner barrel, terminating the injection. This contact with the inner barrel closes the second switch, automatically deactivating the vacuum pump (both switches ON). At this point, the injector is in the uncocked configuration, and after replacing the injected medicament, the above described operation steps can be repeated to perform another injection.